Rviz not loading model

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Hi,

I'm new to ROS and was having a go at a tutorial for using the Clearthpath Husky simulator.

Gazebo works fine, but Rviz for the husky reports an error finding the model. I get this output in the terminal:

Traceback (most recent call last):
  File "/opt/ros/hydro/lib/joint_state_publisher/joint_state_publisher", line 327, in <module>
    jsp = JointStatePublisher()
  File "/opt/ros/hydro/lib/joint_state_publisher/joint_state_publisher", line 25, in __init__
    robot = xml.dom.minidom.parseString(description).getElementsByTagName('robot')[0]
  File "/usr/lib/python2.7/xml/dom/minidom.py", line 1931, in parseString
    return expatbuilder.parseString(string)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 940, in parseString
    return builder.parseString(string)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 223, in parseString
    parser.Parse(string, True)
TypeError: must be string or read-only buffer, not None

I'm using ROS Hydro on Ubuntu 13.04. Haven't been able to find a solution for this, so any help would be greatly appreciated.

Thanks!